Coated cutting tool

ABSTRACT

A coated cutting tool has a CVD coated and a substrate of a cemented carbide, wherein the metallic binder in the cemented carbide includes Ni. The CVD coating has an inner layer of TiN and a subsequent layer of TiCN. The C-activity relative to graphite in the metallic binder is lower than 0.15 and an average d electron value of the metallic binder is 7.00-7.43, wherein an interface between the substrate and the inner TiN layer is free of Ti-containing intermetallic phase.

TECHNICAL FIELD

The present invention relates to a coated cutting tool comprising asubstrate and a coating, wherein the substrate is a cemented carbidewherein the metallic binder in the cemented carbide comprises Ni. Thecoating is a CVD coating comprising an inner layer of TiN and a layer ofTiCN.

BACKGROUND

The market of cutting tools for chip forming metal cutting operations isdominated by CVD (Chemical Vapor Deposition) and PVD (Physical VaporDeposition) coated cemented carbides wherein the cemented carbide isusually made of WC in a metallic binder of Co. Alternative metallicbinders without Co or reduced amount of Co are being developed but arestill rare or non-existing in the products on the market. Not only theproduction of the cemented carbide itself, but also the coating of thecemented carbide is demanding, especially during chemical vapordeposition which is performed using reactive gases at high temperature,since interactions occur between the gas phase and the cemented carbide.

Among the alternative metallic binders Ni is a promising candidate: anelement on the side of Co in the periodic table. Ni shows a highreactivity with Ti and a high amount of Ni in the cemented carbidecauses problems in chemical vapor deposition of a Ti-containing coatingsince intermetallic phases such as Ni3Ti forms at the interface betweenthe cemented carbide and the coating and in the coating. Intermetallicphases such as Ni₃Ti at the interface or in the inner part of theTi-containing coating negatively influence the wear resistance of acoating subsequently deposited on the Ti-containing coating.

The problem of the formation of Ni₃Ti during deposition of a TiN coatingon Ni metal substrates is analyzed in “Chemical vapor deposition of TiNon transition metal substrates” by L. von Fieandt et al, Surface andCoatings Technology 334 (2018) 373-383. It was concluded that theformation of Ni₃Ti could be reduced by an excess of N₂ partial pressureand low H₂ partial pressure during the CVD process.

It is an object of the present invention to provide a coated cuttingtool for metal cutting with a Ni-containing cemented carbide substrateand with a high-performance wear resistant CVD coating. It is a furtherobject to provide a wear resistant coating comprising a TiN layer, aTiCN layer and a 001 oriented α-Al₂O₃ on a Ni containing cementedcarbide substrate, especially a substrate containing a metallic binderwith more than 60 wt % Ni.

DESCRIPTION OF THE INVENTION

At least one of the above-mentioned objects is achieved by a cuttingtool according to claim 1. Preferred embodiments are disclosed in thedependent claims.

The present invention relates to a coated cutting tool comprising asubstrate of cemented carbide and a coating, wherein the cementedcarbide composed of hard constituents in a metallic binder and whereinsaid metallic binder comprises 55 to mol % Ni and 10-35 mol % Co, 4-15mol % W and wherein the coating comprises in order from the substrate aninner TiN layer and a TiCN layer, wherein the C-activity (carbonactivity) relative to graphite in the metallic binder is lower than 0.15and the average d electron value of the metallic binder is 7.0-7.43wherein an interface between the substrate and the inner TiN layer isfree of Ti-containing intermetallic phase.

It was surprisingly found that a high quality of TiN and TiCN can bedeposited on a cemented carbide substrate with a high Ni content in themetallic binder when the average d-electron value in the metallic binderis 7.0-7.43 and the C-activity relative to graphite is below 0.15.Coated cutting tools according to the present invention havesurprisingly shown fewer pores at the inner part of the coating and thisis promising for a wear resistant coating aimed for metal cuttingapplications. The inner TiN and the TiCN layer show improved propertiesrelating to the formation of intermetallic phases, pores anddisturbances relating to the orientation of the layer and subsequentlydeposited layers. Technical effects can be increased flank wearresistance and/or increased flaking resistance and/or increased craterwear resistance in metal cutting operations of for example steel.

The composition of the metallic binder in the cemented carbide have animpact on the quality of a layer deposited by CVD thereon, at least if aTi-containing layer is to be deposited. TiN is a very common initiallayer in cutting tool coatings. Without being bound to any theory theinventors have drawn the conclusion that during a CVD deposition of aTiN layer, N₂-molecules are believed to dissociate into N-atoms/N-radicals before they can react and form TiN. However, Ni in the surfaceincrease the recombination rate of N₂ from N-atoms/radicals and thuspassivates the N and prevents dissociation of N-atoms/radicals on thesurface. Without N-atoms/radicals no TiN can form. Instead Ti mightreact with Ni forming NiTi₃ as described above. The reactivity of Ni inthe metallic binder is influenced by the composition of the metallicbinder. Further, it has been found that the number of d-electrons andthe C-activity in the metallic binder is important.

The average number of d-electrons of the metallic binder is not only setby the components Co, Ni and/or Fe, it is also influenced by othermetallic elements present in the alloy that is the metallic binder. Forexample, the W content have a relatively high impact on the averagenumber of d-electrons in the metallic binder. The W content in thebinder is highly influenced by the C content such that an excess of Cresults in lower W content and a lower C results in a higher W contentin the metallic binder.

The C-activity is a thermodynamic measure of how easy carbon can reactwith other elements. It is expressed as a dimensionless quantity between0 and 1. It is related to the concentration but takes properly intoaccount all physical interactions that limit the whole amount of carbonto react. The definition of carbon activity is

C−activity=exp((μ−μ_(graf))/RT)

where μ is the chemical potential of carbon in the material, μ_(graf) isthe chemical potential of carbon in pure graphite, R is the gas constantand T is the temperature. The carbon activity is a good measure of theposition in the phase diagram, an activity close to 1 means that thecemented carbide is close to having free carbon in the microstructure,whereas a low value, close to 0.1, means that the cemented carbide isprone to having eta phase (Me₆C and Me₁₂C phases) in the microstructure.

Cemented carbide is herein meant a material comprising hard constituentsdistributed in a continuous metallic binder phase. This kind of materialhas properties combining a high hardness from the hard constituents witha high toughness from the metallic binder phase and is suitable as asubstrate material for metal cutting tools. By “cemented carbide” isherein meant a material that comprises at least 50 wt % WC, possiblyother hard constituents common in the art of making cemented carbidesand a metallic binder.

The metallic binder of the cemented carbide can comprise elements thatare dissolved in the metallic binder during sintering, such as W and Coriginating from the WC. Depending on what types of hard constituentsthat are present, also other elements can be dissolved in the binder.

By “cutting tool” is herein meant a cutting tool for metal cutting suchas an insert, an end mill or a drill. The application areas can beturning, milling or drilling.

By intermetallic phase is herein meant a metal alloy of two or moremetallic elements. By Ti-containing intermetallic phase one of thesemetallic elements is Ti. In one embodiment of the present invention theTi-containing intermetallic phase is Ni₃Ti.

Presence of Ti-containing intermetallic phase in the interphase and/orin the part of the TiN layer adjacent to the substrate influences thegrowth of the TiN layer and also of subsequent layers. The intermetallicphases disturb a columnar growth and pores are commonly found incombination with the intermetallic phases. Normally the TiN and thesubsequent TiCN grow with columnar grains, and in an analyze in SEM of asample with intermetallic phases present, a disturbed growth is found.

In one embodiment of the present invention the C-activity in themetallic binder is 0.095-0.12.

In one embodiment of the present invention the interface between thesubstrate and the coating is free of Ti- and Ni-containing intermetallicphase.

In one embodiment of the present invention the average d electron valueis 7.20-7.43.

In one embodiment of the present invention the average d electron valueis 7.30-7.43.

In one embodiment of the present invention the metallic binder comprises65 to 80 mol % Ni and 10-25 mol % Co, 8-13 mol % W.

5 In one embodiment of the present invention the metallic binder contentin the cemented carbide is 3-20 wt %, preferably 5-15 wt %, mostpreferably 7-12 wt %.

In one embodiment of the present invention the total thickness of thecoating is 2-20 μm. The coating is preferably a CVD coating.

In one embodiment of the present invention the thickness of the TiNlayer is 0.1-1 μm, preferably deposited on the cemented carbidesubstrate.

In one embodiment of the present invention the thickness of the TiCNlayer is 6-12 μm.

In one embodiment of the present invention the wherein the coatingcomprises an α-Al₂O₃ layer located between the TiCN layer and anoutermost surface of the coated cutting tool.

In one embodiment of the present invention the thickness of the Al₂O₃layer located between the TiCN layer and an outermost surface of thecoated cutting tool is 4-8 μm.

In one embodiment of the present invention the α-Al₂O₃ layer exhibits atexture coefficient TC(h k l), as measured by X-ray diffraction usingCuKα radiation and θ-2θ scan, defined according to Harris formula

$\begin{matrix}{{{TC}({hkl})} = {\frac{I({hkl})}{I_{0}({hkl})}\lbrack {\frac{1}{n}{\sum_{n = 1}^{n}\frac{I({hkl})}{I_{0}({hkl})}}} \rbrack}^{- 1}} & (1)\end{matrix}$

where I(h k l) is the measured intensity (integrated area) of the (h kl) reflection, I₀(h k l) is the standard intensity according to ICDD'sPDF-card No. 00-010-0173, n is the number of reflections used in thecalculation, and where the (h k l) reflections used are (1 0 4), (1 10), (1 1 3), (024), (1 1 6), (2 1 4), (3 0 0) and (0 0 12), wherein TC(00 12)≥6, preferably ≥7.

In one embodiment of the present invention the coating further comprisesone or more layers selected from TiN, TiCN, AlTiN, ZrCN, TiB₂, Al₂O₃, ormultilayers comprising α-Al₂O₃ and/or κ-Al₂O₃.

In one embodiment of the present invention the cemented carbidesubstrate comprises eta phase. By eta phase is herein meant carbidesselected from Me₆C and Me₁₂C where Me is selected from W and one or moreof the binder phase metals. Common carbides are W₆Co₆C, W₃Co₃C, W₆Ni₆C,W₃Ni₃C, W₆Fe₆C, W₃Fe₃C.

In on embodiment the cemented carbide substrate comprises carbides,carbonitrides or nitrides of one or more of Ti, Ta, Nb, Cr, Mo, Zr or V.

BRIEF DESCRIPTION OF DRAWINGS

Embodiments of the invention and also references will be described withreference to the accompanying drawings, wherein:

FIG. 1 is a cross-sectional SEM micrograph showing the substrate coatinginterface of a coated cutting tool, NC60e with the coating of CVDprocess 1 (invention),

FIG. 2 is a cross-sectional SEM micrograph showing the substrate coatinginterface of a coated cutting tool, NC70e with the coating of CVDprocess 1 (invention),

FIG. 3 is a cross-sectional SEM micrograph showing the substrate coatinginterface of a coated cutting tool, NC70e with the coating of CVDprocess 2 (invention),

FIG. 4 is a cross-sectional SEM micrograph showing the substrate coatinginterface of a coated cutting tool, NC80e with the coating of CVDprocess 1 (reference),

FIG. 5 is a cross-sectional SEM micrograph showing the substrate coatinginterface of a coated cutting tool, NC80e with the coating of CVDprocess 2 (invention),

FIG. 6 is a cross-sectional SEM micrograph showing the substrate coatinginterface of a coated cutting tool, N100e with the coating of CVDprocess 1 (reference),

FIG. 7 is top view SEM micrograph showing the outer surface of a coatedcutting tool, substrate NC70e with the coating of CVD process 2(invention),

FIG. 8 is top view SEM micrograph showing the outer surface of a coatedcutting tool, substrate N100e with the coating of CVD process 2(reference).

METHODS

The cemented carbide substrate of the invention can be made according tothe following steps:

-   -   providing powders forming or being hard constituents such as W,        Ta, Cr, C, WC, TiC, etc.    -   providing powders forming metallic binder such as Co, Ni    -   providing milling liquid    -   milling, drying, pressing and sintering the powders into        cemented carbide substrates.

During sintering oxygen will react with carbon and leave the substrateas CO or CO₂. Exactly how much carbon that is lost during sinteringdepends on the raw material and production techniques used and it is upto the person skilled in the art to adjust the amount of each componentso that the aimed sintered material is achieved.

The C content in the cemented carbide was analyzed with carboncombustion analysis in a LECO 844 Series instrument. The C content inthe cemented carbide is measured in the sintered substrate. Some of theC that is mixed in the powder during the production of the cementedcarbide is consumed during sintering, some carbon can dissolve in themetallic binder and some carbon might form carbides.

The present invention is related to the composition of the metallicbinder, and since it is expensive and complicated to produce samples thecomposition was calculated with a software called Thermo-Calc. Thecomposition of the metallic binder can alternatively be measured withXRF (X-ray fluorescence).

Thermo-Calc is a software package that is world-wide used by materialscientists, researchers and industry in the field of materialsengineering for development and production of both materials andcomponents. The development of the Thermo-Calc software was startedalready in the mid 70's at the department for physical metallurgy at theRoyal Institute of Technology in Stockholm, Sweden, and in 1997Thermo-Calc Software AB was founded. More information can be found at:www.thermocalc.com. Thermo-Calc provides for example thermodynamiccalculations of the amounts of phases and their compositions and thephase diagrams (binary, ternary and multi-component).

The calculations made with Thermo-Calc are based on thermodynamic datawhich is supplied in high-quality databases for various purposes thatinclude many different materials. The databases are produced by expertsthrough assessment and systematic evaluation of experimental andtheoretical data, following the well-established so-called CALPHADtechnique. The databases provided by Thermo-Calc Software AB arevalidated against experimental data to evaluate their accuracy in thecalculated predictions.

The database used herein for the Thermo-Calc calculations was “TCFE7”commercially available from Thermo-Calc Software AB. TCFE7 is athermodynamic database for different kinds of steels, Fe-based alloys(stainless steels, high-speed steels, tool steels, HSLA steels, castiron, corrosion-resistant high strength steels and more) and cementedcarbides. The TCFE7 database is validated against experimental data andshows accurate predictions, among others, for cemented carbides,especially in predicting correct phases and fractions, phasecompositions and solid/liquid equilibrium temperatures.

The composition of the metallic binder in the present invention wasdetermined using Thermo-Calc software which is further described in[J.-O. Andersson, T. Helander, L. Hoglund, P. Shi, and B. Sundman,Thermo-Calc & DICTRA, computational tools for material science, Calphad,2002:26(2):273312].

The Thermo-Calc calculations of the present invention was made with thecriterions: atmospheric pressure, a temperature of 1000° C., one mole ofsubstance, weighed in compositions of Ni, Fe, and Co with the additionof milled in Co, C level from chemical analysis and balance of W.

When the composition of the metallic binder, in mol %, is known theaverage number of d electrons is calculated as follows: The d-electronsare counted as the number of electrons in the highest d-orbital perelement, e.g. 6 for Fe, 7 for Co, 8 for Ni, 0 for C, and 4 for W.

The coatings in the examples below were deposited in a radial IonbondBernex™ type CVD equipment 530 size capable of housing 10000 half-inchsize cutting inserts.

In order to investigate the texture of the layer(s) X-ray diffractionwas conducted on the flank face and the rake face of cutting toolinserts using a Xpert-Pro diffractometer system equipped with aX'Celerator RTMS detector type. The coated cutting tool inserts weremounted in sample holders to ensure that the surface of the cutting toolinserts was parallel to the reference surface of the sample holder andalso that the cutting tool surface was at appropriate height. Cu-Kαradiation was used for the measurements, with a voltage of 45 kV and acurrent of 40 mA. A 0.02 radian soller slit and a 0.25 degree divergenceslit were used for the incident beam path. For the diffracted beam a0.25 degree anti-scatter slit and 0.02 radian soller slit were used. TheBeta-filter Nickel had a thickness of 0.020 mm. The diffracted intensityfrom the coated cutting tool was measured in the range 15° to 140° 2θ,i.e. over an incident angle θ range from 10 to 70°.

The data analysis, including background subtraction, Cu-K_(α2) strippingand profile fitting of the data, was done using PANalytical's X'PertHighScore Plus software. A general description of the fitting is made inthe following. The output (integrated peak areas for the profile fittedcurve) from this program was then used to calculate the texturecoefficients of the layer by comparing the ratio of the measuredintensity data to the standard intensity data according to a PDF-card ofα-Al₂O₃, using the Harris formula (1) as disclosed above. Since thelayer is finitely thick the relative intensities of a pair of peaks atdifferent 2θ angles are different than they are for bulk samples, due tothe differences in path length through the layer. Therefore, thin filmcorrection was applied to the extracted integrated peak area intensitiesfor the profile fitted curve, taken into account also the linearabsorption coefficient of layer, when calculating the TC values. Sincepossible further layers above the α-Al₂O₃ layer will affect the X-rayintensities entering the α-Al₂O₃ layer and exiting the whole coating,corrections need to be made for these as well, taken into account thelinear absorption coefficient for the respective compound in a layer.Alternatively, a further layer, such as TiN, above an alumina layer canbe removed by a method that does not substantially influence the XRDmeasurement results, e.g. chemical etching.

In order to investigate the texture of the α-Al₂O₃ layer X-raydiffraction was conducted using CuK_(α) radiation and texturecoefficients TC (h k l) for different growth directions of the columnargrains of the α-Al₂O₃ layer were calculated according to Harris formula(1), where I(h k l)=measured (integrated area) intensity of the (h k l)reflection, I₀(h k l)=standard intensity according to ICDD's PDF-card no00-010-0173, n=number of reflections to be used in the calculation. Inthis case the (h k l) reflections used are: (1 0 4), (1 1 0), (1 1 3),(0 2 4), (1 1 6), (2 1 4), (3 0 0) and (0 0 12).

It is to be noted that peak overlap is a phenomenon that can occur inX-ray diffraction analysis of coatings comprising for example severalcrystalline layers and/or that are deposited on a substrate comprisingcrystalline phases, and this has to be considered and compensated for.An overlap of peaks from the α-Al₂O₃ layer with peaks from the TiCNlayer might influence measurement and needs to be considered. It is alsoto be noted that for example WC in the substrate can have diffractionpeaks close to the relevant peaks of the present invention.

EXAMPLES

Exemplifying embodiments of the present invention will now be disclosedin more detail and compared to reference embodiments. Coated cuttingtools (inserts) were manufactured and analyzed.

Cemented carbide substrates of ISO-type SNUN120408 were manufactured.The cemented carbide substrates were manufactured with WC in a metallicbinder, wherein the metallic binder content was about 10 wt %. Thecemented carbide substrates were manufactured from a powder mixture. Thepowder mixture was milled, dried, pressed and sintered at 1450° C. WC/Comilling bodies were used during the milling and mixing step. The amountcarbon in the powder was about 6.07 wt %, while the amount carbon asmeasured in chemical analysis of the sintered cemented carbide ispresented in table 1A and 1B. The sintered cemented carbide comprisedabout 0.4 wt % Co originating mainly from the milling bodies that wereworn during the milling step. No free graphite was visible in a SEMmicrograph of a cross section of the cemented carbide substrates.

The C level of the substrates was measured with LECO carbon combustion.The compositions of the cemented carbide substrates are listed in wt %in table 1A, so called e-samples, and 1B, so called f-samples.

TABLE 1A Summary of cemented carbide substrates, e-samples Ni Co C WSubstrate [wt %] [wt %] [wt %] [wt %] NC50e 4.99 5.41 5.19 84.41 NC60e5.99 4.41 5.23 84.37 NC70e 6.99 3.41 5.21 84.39 NC80e 7.99 2.41 5.2284.38 NC90e 9.00 1.40 5.20 84.40 N100e 10.05  0.40 5.16 84.39

TABLE 1B Summary of cemented carbide substrates, f-samples Ni Co C WSubstrate [wt %] [wt %] [wt %] [wt %] NC50f 4.99 5.41 5.37 84.23 NC60f5.99 4.41 5.35 84.25 NC70f 6.99 3.41 5.37 84.23 NC80f 7.99 2.41 5.3784.23 NC90f 9.00 1.40 5.34 84.26 N100f 10.16  0.40 5.29 84.15

The composition of the metallic binder was calculated with Thermo-Calcusing the following conditions: atmospheric pressure, a temperature of1000° C., one mole of substance, weighed in compositions of Ni, Fe, andCo with the addition of milled in Co, C level from chemical analysis andbalance of W. The resulting binder compositions, excluding carbides, arelisted in mol % in table 2A (e-samples) and 2B (f-samples).

To calculate the average number of d-electrons in the binder, thecalculated composition of the metallic binder is used. The d-electronsare counted as the number of electrons in the highest d-orbital perelement, e.g. 7 for Co, 8 for Ni, 0 for C, and 4 for W. The averagenumber of d electrons in the binders are presented in table 2A and 2B.

To calculate the carbon activity of the cemented carbide, first thechemical composition must be known. In the present examples theC-activity calculation is based on the values presented in Tables 1A and1B. In an unknown sample, this can be measured by means of e.g. XRF.

A Thermo-Calc calculation of the thermodynamic equilibrium is performedat, atmospheric pressure, a temperature of 1000° C., one mole ofsubstance, compositions of Ni, Fe, Co, and C from chemical analysis andbalance of W. The carbon activity relative to graphite at thisequilibrium is then extracted as an output parameter from Thermo-Calc,see Tables 2A and 2B.

TABLE 2A Summary of metallic binder, e-samples Average Ni Co C W number[mol [mol [mol [mol of d C- Substrate %] %] %] %] electrons activityNC50e 42.75 45.85 0.18 11.22 7.08 0.113 NC60e 51.15 37.43 0.17 11.257.16 0.111 NC70e 59.67 28.84 0.17 11.31 7.25 0.108 NC80e 68.01 20.330.18 11.48 7.32 0.106 NC90e 76.22 11.76 0.19 11.83 7.39 0.102 N100e84.08 3.28 0.21 12.43 7.45 0.098

TABLE 2B Summary of metallic binder, f-samples Average Ni Co C W number[mol [mol [mol [mol of d C- Substrate %] %] %] %] electrons activityNC50f 44.83 48.41 0.47 6.30 7.23 0.390 NC60f 53.38 39.14 0.39 7.10 7.290.320 NC70f 64.30 27.92 0.38 7.40 7.39 0.429 NC80f 71.63 21.48 0.54 6.357.49 0.454 NC90f 79.59 12.37 0.46 7.58 7.54 0.334 N100f 87.05 3.41 0.419.12 7.57 0.240

CVD coatings were deposited on the cemented carbide compositionspresented in Table 2A and Table 2B and a summary of the CVD coatings aregiven in Table 3. Prior to the coating deposition the rake faces werepolished to remove the outermost metal from the surfaces, the flank facewas left unpolished. The polishing was performed by mounting each ofSNUN120408 samples in a black conductive phenolic resin from AKASELwhich were afterwards ground down about 1 mm and then polished in twosteps: rough polishing (9 μm) and fine polishing (1 μm) using a diamondslurry solution. After polishing the SNUN120408 sample were taken outfrom the black conductive phenolic resin and washed in ethanol beforecoating.

TABLE 3 Summary of CVD processes TiN bonding α- total TiCN layer Al₂O₃CVD process TiN-1 TiN-2 [μm] [μm] [μm] [μm] Process CVD 1 No Yes 0.2 8.50.9 5.4 (normal) Process CVD 2 Yes Yes 0.7 10 0.9 5.2 (modified)

Before starting the CVD deposition the CVD chamber was heated up toreach 885° C. The pre-heating step was performed at 1000 mbar and in 100vol % H₂ for both Process CVD 1 and Process CVD 2.

In the Process CVD 1 the substrates were first coated with an about0.2-0.3 μm thick TiN-layer at 885° C., process TiN-2. In the Process CVD2 two alternative depositions of TiN were performed: an initial step ofTiN-1 followed by process TiN-2. The aim of the TiN-1 step is to preventintermetallic phases such as Ni₃Ti from forming in the CVD coating andat the substrate-coating interface. During the TiN-1 deposition the N₂partial pressure was high and the H₂ partial pressure was low, and HClwas added, as compared to the TiN-2 deposition step which was performedwithout HCl and with a 50/50 relation for the H₂/N₂ gasses. When theTiN-1 was deposited, the subsequent TiN-2 deposition time was adapted toreach a total TiN layer thickness of 0.7 μm. The TiN-1 deposition wasrun for 150 minutes.

Thereafter an approximately 8 μm TiCN layer was deposited by employingthe well-known MTCVD technique using TiCl₄, CH₃CN, N₂, HCl and H₂ at885° C. The volume ratio of TiCl₄/CH₃CN in an initial part of the MTCVDdeposition of the TiCN layer was 6.6, followed by a period using a ratioof TiCl₄/CH₃CN of 3.7. The details of the TiN and the TiCN depositionare shown in Table 4.

TABLE 4 MTCVD of TiN and TiCN MT CVD of H₂ N₂ HCl TiCl₄ CH₃CN TiN andTiCN Pressure [vol [vol [vol [vol [vol (885° C.): [mbar] %] %] %] %] %]TiN-1 1000 10.5 87.4 0.88 1.25 — TiN-2 400 48.8 48.8 — 2.44 — TiCN inner55 59.0 37.6 — 2.95 0.45 TiCN outer 55 81.5  7.8 7.8  2.38 0.65

After the deposition of the TiCN outer layer the temperature wasincreased from 885° C. to 1000° C. in an atmosphere of 75 vol % H₂ and25 vol % N₂ at 55 mbar for the Process CVD 1 After the deposition of theTiCN outer layer the temperature was increased from 885° C. to 1000° C.in an atmosphere of 100 vol % N₂ at 1000 mbar for the Process CVD 2.

A 1-2 μm thick bonding layer was deposited at 1000° C. on top of theMTCVD TiCN layer by a process consisting of four separate reactionsteps. First a HTCVD TiCN step using TiCl₄, CH₄, N₂, HCl and H₂ at 400mbar, then a second step (TiCNO-1) using TiCl₄, CH₃CN, CO, N₂ and H₂ at70 mbar, then a third step (TiCNO-2) using TiCl₄, CH₃CN, CO, N₂ and H₂at 70 mbar and finally a fourth step (TiN-3) using TiCl₄, N₂ and H₂ at70 mbar. Prior to the start of the subsequent Al₂O₃ nucleation, thebonding layer was oxidized for 4 minutes in a mixture of CO₂, CO, N₂ andH₂.

The details of the bonding layer deposition are shown in Table 5.

TABLE 5 Bonding layer deposition Pres- H₂ N₂ CH₄ HCl CO TiCl₄ CH₃CN CO₂Bonding sure [vol [vol [vol [vol [vol [vol [vol [vol layer [mbar] %] %]%] %] %] %] %] %] HTCVD 400 67.9 25.5 3.4 1.7 — 1.55 — — TiCN TiCNO-1 7083.7 12.0 — 1.2 1.2 1.5 0.40 — TiCNO-2 70 63.1-61.1 31.5-30.6 — —1.6-4.6 3.15-3.06 0.65-0.63 — TiN-3 70 64.5 32.3 — — — 3.23 — — Oxida-55 53.8 30 — — 12.5 — — 3.7 tion

On top of the bonding layer an α-Al₂O₃ layer was deposited. All theα-Al₂O₃ layers were deposited at 1000° C. and 55 mbar in two steps. Thefirst step using 1.2 vol-% AlCl₃, 4.7 vol-% CO₂, 1.8 vol-% HCl andbalance H₂ giving about 0.1 μm α-Al₂O₃ and a second step as disclosedbelow giving a total α-Al₂O₃ layer thickness of about 5 μm. The secondstep of the α-Al₂O₃ layer was deposited using 1.2% AlCl₃, 4.7% CO₂, 3.0%HCl, 0.58% H₂S and balance H₂.

XRD was used to analyse the texture coefficient (TC) values of theα-Al₂O₃ in accordance with the method as disclosed above. The layerthicknesses were analyzed in a Carl Zeiss AG -Supra 40SEM (ScanningElectron Microscope) type by studying a cross section of each coating at12000×magnification and both the bonding layer and the initial TiN layerare included in the TiCN layer thickness, see Table 1. Both the polishedrake face and the unpolished flank face were studied. The results fromthe XRD are presented in Table 6A and 6B.

TABLE 6A XRD results (e-samples) TC(0 0 12) of α-Al₂O₃ TC(0 0 12) ofα-Al₂O₃ flank face polished rake face Process Process Process ProcessSample CVD 1 CVD 2 CVD 1 CVD 2 NC70e 6.10 Not analyzed 7.54 7.72 NC80e7.01 Not analyzed Not analyzed 7.75 NC90e 7.29 6.01 Not analyzed 7.61

TABLE 6B XRD results (f-samples) TC(0 0 12) of α-Al₂O₃ TC(0 0 12) ofα-Al₂O₃ flank face polished rake face Process Process Process ProcessSample CVD 1 CVD 2 CVD 1 CVD 2 NC60f 6.80 Not analyzed Not analyzed Notanalyzed NC70f 6.63 Not analyzed 7.32 7.66 NC80f 5.95 Not analyzed Notanalyzed 7.00 NC90f Not analyzed Not analyzed 0.00 4.69

The coatings were also analyzed using SEM to study the presence of anyNi compounds such as intermetallic phases at the interface betweensubstrate and the first TiN layer.

Top view images of the coated samples showed an unevenness or highsurface roughness on the outer surface of the alumina. It was concludedthat formation of intermetallic phases at the interface could beidentified by studying the outer surface of the alumina in that anunexpectedly rough surface indicated intermetallic phases at theinterface.

Cross section images were mainly focused at the interface between thesubstrate and the first TiN layer to determine if diffusion of binderelements (Ni compounds) had disturbed the growth of the coating.Occurrence of Ti-containing intermetallic phases (such as Ni₃Ti)depended on the binder composition.

The coating quality deposited in the Process CVD 1 and the Process CVD 2on Ni rich binders was determined by analyzing both the outer surfaceand morphology of Al₂O₃ and also the interface between substrate and thefirst TiN layer. Unevenness of Al₂O₃ surface can be result from growthof coarse grains and correlates with the formation of intermetallicphases such as Ni₃Ti formed at the interface between the substrate andthe coating. When the unevenness of the Al₂O₃ was difficult to determinethe interface between the substrate and coating was analyzed todetermine the coating quality. For this investigation, SEM was used at12000×magnification and 3 parallel images were studied from 3 places onthe sample approximatively 10 μm apart along the substrate surface inorder to detect presence of intermetallic phases. The results of theanalyses are shown in Tables 7A and 7B.

TABLE 7A SEM analyse of e-samples Ti-containing intermetallic Visualunevenness or high phases identified in interface surface roughness onouter (cross section) surface of alumina (top view) Process ProcessProcess Process Sample CVD 1 CVD 2 CVD 1 CVD 2 NC50e No Not analyzed NoNo NC60e No Not analyzed No No NC70e No No No No NC80e Yes No Yes NoNC90e Yes Not analyzed Yes No N100e Yes Not analyzed Not analyzed Yes

TABLE 7B SEM analyse of f-samples Ti-containing Visual unevenness orintermetallic phases high surface roughness identified in interface onouter surface of (SEM cross section) alumina (SEM top view) ProcessProcess Process Process Sample CVD 1 CVD 2 CVD 1 CVD 2 NC50f No Notanalyzed No No NC60f No Not analyzed No No NC70f No No No No NC80f YesYes Yes Yes NC90f Yes Not analyzed Yes Yes N100f Yes Not analyzed YesYes

It is clear from the surface analysis and the cross section analysisthat samples showing visual unevenness or high surface roughness on theouter surface of the alumina (top view) also showed Ti-containingintermetallic phases in the interface (cross section). It is unexpectedthat no Ti-containing intermetallic phases or disturbing pores appearsat the interface of the CVD coating when the C-activity is low, lowerthan 0.15, and the average number of d electrons are 7.0-7.43, see Table8.

TABLE 8 Summary of results Substrate e-samples f-samples partial named-electrons C-activity d-electrons C-activity NC50 7.08*  0.113 7.23* 0.390 NC60 7.16*  0.111 7.29*  0.320 NC70 7.25*  0.108 7.39**  0.429NC80 7.32**  0.106 7.49**  0.454 NC90 7.39**  0.102 7.54*** 0.334 N1007.45*** 0.098 7.57*** 0.240 *No Ti-containing intermetallic phasespresent at interface **CVD process 1: Ti-containing intermetallic phasesat interface, CVD process 2: no Ti-containing intermetallic phases atinterface ***Ti-containing intermetallic phases at interface

While the invention has been described in connection with variousexemplary embodiments, it is to be understood that the invention is notto be limited to the disclosed exemplary embodiments; on the contrary,it is intended to cover various modifications and equivalentarrangements within the appended claims.

1. A coated cutting tool comprising a substrate of cemented carbide anda coating, wherein the cemented carbide includes hard constituents in ametallic binder and wherein said metallic binder comprises 55 to 80 mol% Ni and 10-35 mol % Co, 4-15 mol % W and wherein the coating comprisesin order from the substrate an inner TiN layer and a TiCN layer, whereinC-activity relative to graphite in the metallic binder is lower than0.15 and an average d electron value of the metallic binder is 7.00-7.43wherein an interface between the substrate and the inner TiN layer isfree of Ti-containing intermetallic phase.
 2. The coated cutting tool ofclaim wherein the C-activity in the metallic binder is 0.095-0.120. 3.The coated cutting tool of claim 1, wherein the interface between thesubstrate and the inner TiN layer is free of Ti- and Ni-containingintermetallic phase.
 4. The coated cutting tool of claim 1, wherein theaverage d electron value is 7.20-7.43.
 5. The coated cutting tool ofclaim 1, wherein the average d electron value is 7.30-7.43.
 6. Thecoated cutting tool of claim 1, wherein the metallic binder includes 65to 80 mol % Ni and 10-25 mol % Co, 8-13 mol % W.
 7. The coated cuttingtool of claim 1, wherein the metallic binder content in the cementedcarbide is 3-20 wt %.
 8. The coated cutting tool of claim 1, wherein atotal thickness of the coating is 2-20 μm.
 9. The coated cutting tool ofclaim 1, wherein the coating is a CVD coating.
 10. The coated cuttingtool of claim 1, wherein a thickness of the TiN layer is 0.1-1 μm,deposited on the cemented carbide substrate.
 11. The coated cutting toolof claim 1, wherein a thickness of the TiCN layer is 6-12 μm.
 12. Thecoated cutting tool of claim 1, wherein the coating includes an α-Al₂O₃layer located between the TiCN layer and an outermost surface of thecoated cutting tool.
 13. The coated cutting tool of claim 1, wherein athickness of the α-Al₂O₃ layer located between the TiCN layer and anoutermost surface of the coated cutting tool is 4-8 μm.
 14. The coatedcutting tool of claim 1, wherein said α-Al₂O₃ layer exhibits a texturecoefficient TC(h k l), as measured by X-ray diffraction using CuKαradiation and θ-2θ scan, defined according to Harris formula${{TC}({hkl})} = {\frac{I({hkl})}{I_{0}({hkl})}\lbrack {\frac{1}{n}{\sum\limits_{n = 1}^{n}\frac{I({hkl})}{I_{0}({hkl})}}} \rbrack}^{- 1}$where I(h k l) is the measured intensity (integrated area) of the (h kl) reflection, I₀(h k l) is the standard intensity according to ICDD'sPDF-card No. 00-010-0173, n is the number of reflections used in thecalculation, and where the (h k l) reflections used are (1 0 4), (1 10), (1 1 3), (0 2 4), (1 1 6), (2 1 4), (3 0 0) and (0 0 12), whereinTC(0 0 12)≥6.
 15. The coated cutting tool of claim 1, wherein the CVDcoating further comprises one or more layers selected from TiN, TiCN,AlTiN, ZrCN, TiB₂, Al₂O₃, or multilayers comprising α-Al₂O₃ and/orκ-Al₂O₃.